“Ace didn’t master his devil fruit” Ace had a very good mastery of his fruit just look at the versatility of his attacks, also when Ace was on Drum Island the town’s people told Luffy’s crew it didn’t snow that entire day, which is strange because Drum Island is known for snowing every day, this hints at Ace having awakening abilities.
“Ace is physically weak” Van Augur comments that even without the Mera Mera no Mi devil fruit his physical abilities are impressive as expected of a Whitebeard Commander. Ace fought off Jinbe for 5 DAYS which is extremely physically overwhelming, showing Ace has incredible levels of stamina, only top tiers have been shown to fight for days e.g. Admirals, Shanks, Mihawk etc even Luffy’s longest battle has only been 12 hours or so.
“Ace was devil fruit reliant and his haki was weak” It’s been revealed through the Ace novels that Ace could use Armament Haki, which he awakened mid-fight against a vice admiral and it was STRONGER than the vice admiral’s own haki after just awakening it, there’s no telling how much stronger it would have gotten after 3 years of New World battles. We already knew he had Conqueror’s Haki, which he awakened as KID!! May I remind you when Luffy awakened it at 17 years old showing the difference in natural talent between Ace and Luffy. In fact his haki was so powerful in the Ace novel, when Ace steps onto the snowy Island where Shanks is, Shanks comments “his haki is like fire which is why the snow on the island is melting”.